For a few crucial weeks each spring, bees are the most essential labourers on earth, pollinating many of the world's major fruit crops: their survival through winter is fundamental for agriculture. Realising that the survival of the individual was key to a colony's success, Gro Amdam became intrigued by bee longevity. Worker bees' lifespans tend to be only a few weeks; however, Amdam explains that a new type of bee develops towards the end of the summer, known as diutinus bees. These bees have an amazing lifespan of 6 months or more and ensure the colony's survival through winter. Curious to find out what limits worker bees' lifespans and allows the development of diutinus bees, Amdam began investigating bee longevity.
Reading the literature, she realised that an egg protein, vitellogenin, could be essential for diutinus bee longevity: which is curious, because diutinus bees are mostly sterile, do not produce eggs and should not need an egg protein. Another thing that became clear was that the presence of brood (young) in a colony was sufficient to prevent worker bees developing into the long-lived veterans. ‘Brood is to diutinus bees what kryptonite is to Superman,’ laughs Amdam. At first Amdam thought that the hard labour of feeding larvae was preventing worker bees from building up their vitellogenin levels and developing into diutinus bees. But then she read a report that the smell of yeast affects the lifespan of fruit flies. Could the smell of brood — brood pheromone — affect the bees' longevity? Could the pheromone prevent workers from building up their vitellogenin levels and developing into long-lived diutinus bees? Amdam decided to investigate whether brood pheromone could be the key to the worker bees' short lifespan (p. ).
Working with Claus Kreibich, and Margrethe Brynem, Amdam's student — Bente Smedal — set up 12 hives where the team could carefully control the levels of brood and brood pheromone to find out whether the worker bees' low vitellogenin levels, and short life expectancy, were due to burn out or the brood's pheromone smell. Providing the worker bees in each hive with a caged queen (that could not produce brood) so that Smedal could control each colony's brood and pheromone levels, she took control of the hive's brood supply, providing the bees with: brood; synthetic brood pheromone; both brood and the synthetic pheromone; or neither brood nor pheromone.
Monitoring the bees' vitellogenin levels 3-4, 7-8 and 23-24 days after establishing the hives, it was clear that being around brood lowered the worker bees' vitellogenin levels. But exposure to the brood pheromone alone also reduced the bees' vitellogenin levels by the same amount. And when Smedal looked at the vitellogenin levels in the 23-24 day old bees, the bees that had been deprived of both the brood and its pheromone had the highest levels of vitellogenin, just like autumn bees embarking on a winter in the colony. Hard labour caring for the brood did not explain the workers' low vitellogenin levels.
And when Brynem checked the hives 200 days later to find out which colonies had survived and which had died, colonies that had not experienced brood or pheromone had survived best, while the hives that had been provided with both brood and pheromone had the worst survival rates. It was the smell of brood — brood pheromone — that regulated the bees' vitellogenin levels and longevity.
